Vapor recovery equipped fuel dispensers, particularly gasoline dispensers, have been known for quite some time, and have been mandatory in areas that are required to do so by the Clean Air Act Amendments passed by the United States Congress. The primary purpose of a vapor recovery system is to recover vapors displaced from a vehicle's fuel tank during a fueling process that would otherwise be emitted to the atmosphere. As liquid gasoline is pumped into the tank, the vapor is displaced and forced out through the vehicle filler pipe. Other volatile hydrocarbon liquids raise similar issues. In addition to the need to recover vapors, some states, and California in particular, are requiring extensive reports about the efficiency with which vapor is recovered.
A traditional vapor recovery system is known as the "balance" system, in which a sheath or boot encircles the liquid fueling spout and connects by tubing back to the fuel reservoir. As the liquid enters the tank, the vapor is forced into the sheath and back toward the fuel reservoir or underground storage tank (UST) where the vapors can be stored or recondensed. Balance systems have numerous drawbacks, including cumbersomeness, difficulty of use, ineffectiveness when seals are poorly made, and slow fueling rates.
As a dramatic step to improve on the balance systems, Gilbarco, Inc., assignee of the present invention, patented an improved vapor recovery system for fuel dispensers, as seen in U.S. Pat. No. 5,040,577, now Reissue Pat. No. 35,238 to Pope, which is herein incorporated by reference in its entirety. The Pope patent discloses a vapor recovery apparatus in which a vapor pump is introduced in the vapor return line and is driven by a variable speed motor. The liquid flow line includes a pulser, conventionally used for generating pulses indicative of the liquid fuel being pumped. This permits computation of the total sale and the display of the volume of liquid dispensed and the cost in a conventional display, such as shown in U.S. Pat. No. 4,122,524 to McCrory et al. A microprocessor translates the pulses indicative of the liquid flow rate into a desired vapor pump operating rate. The effect is to permit the vapor to be pumped at a rate correlated with the liquid flow rate so that, as liquid is pumped faster, vapor is also pumped faster.
There are three basic embodiments used to control vapor flow during fueling operations. A first embodiment is the use of a constant speed vapor pump during fueling without any sort of control mechanism. A second is the use of a pump driven by a constant speed motor coupled with a controllable valve to extract the desired amount of vapor from the vehicle gas tank. While the speed of the pump is constant, the valve may be adjusted to increase or decrease the flow of vapor. A third is the use of a variable speed motor and pump as described in the Pope patent, which is used without a controllable valve assembly. All of these techniques have advantages either in terms of cost or effectiveness. Depending on the reasons driving the installation, any of the three may be appropriate, however none of the three systems, or the balance system as currently implemented by the dispenser manufacturers, are able to provide all the diagnostic information that may be required in the future. The present state of the art is well shown in commonly owned U.S. Pat. No. 5,345,979, which is herein incorporated by reference in its entirety.
The amount of vapor produced during the fueling process is a function of the fuel rate. By way of example, a dispensing rate of two gallons of fuel per minute should emit more vapor than a dispensing rate of one gallon of fuel per minute. Because the fuel rate is known, the expected amount of vapor recovery may also be determined. Present systems place a sensor within the vapor recovery line for determining the amount of vapor within the vapor recovery line. However, these sensors are often used to determine whether the vehicle receiving fuel has an on-board vapor recovery system (ORVR). Another current use is for adjusting the speed of the vapor pump. If the amount of vapor determined by the sensor is not equal to the expected vapor for the amount of fuel being dispensed, the system will alter the speed of the vapor pump, or adjust the valve within the recovery line to obtain the expected results.
A drawback of these existing systems is there is no means for determining whether the vapor recovery system is effectively operating. One problem occurs if there is a leak in the vapor recovery system. Outside air is captured through the leak and drawn into the UST, instead of the vapors emanating from the fuel tank during the fueling process. Leaks in the vapor recovery system are especially problematic in the hanging hardware along the nozzle, hose, and swivel connections. Presently existing systems recognize that not enough vapor is being recovered, and increase the speed of the vapor pump. However, this results in more outside air being pulled into the UST, and does not have any effect on fixing or even indicating that there is a leak.
Another problem occurs when the vapor recovery system draws fuel during the fueling event into the UST. This may occur when the vapor recovery system draws fuel from the user's tank either during or after it has been dispensed. Another situation occurs if there is a leak within the fuel delivery line within the hanging hardware as the fuel leaks from the delivery line directly into the vapor recovery line which is in close proximity. In either of these situations, the fuel has passed through the pulser, the dispenser indicates the fuel has been delivered, and the user is paying for the fuel. Additionally, the vapors emanating during the fueling event are not being captured as the capacity of the recovery line is taken by the leaking fuel.
It is important that the problem of air leaking into the vapor recovery system, or fuel being pulled through the system is recognized. Thus, there remains a need for the sensors placed within the vapor recovery line to be used for diagnostic purposes for determining whether the vapor recovery system is operating effectively.